在Swift 2的闭包内部未分配类属性

Question

我在为Swift类中的属性分配值时遇到麻烦。 该属性在类内部可以正常打印，但是当调用在主viewController中分配属性的类方法时，从外部访问该属性将返回nil 。 这是我的班级定义。

import Foundation

class NetworkConnection {

    var jsonObj: AnyObject?

    func makeHTTPRequest(data: String, location: String, completion: (jsonData: AnyObject?, error: NSError?) -> Void){

        var jsonData: AnyObject!

        let post: NSString = "data=\(data)"
        let url = NSURL(string: location)!
        let postData = post.dataUsingEncoding(NSUTF8StringEncoding)!

        let postLength = String(postData.length)
        let request = NSMutableURLRequest(URL: url)
        request.HTTPMethod = "POST"
        request.HTTPBody = postData
        request.setValue(postLength, forHTTPHeaderField: "Content-Length")
        request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
        request.setValue("application/json", forHTTPHeaderField: "Accept")

        let session = NSURLSession.sharedSession()

        let task = session.dataTaskWithRequest(request) { urlData, response, responseError in

            if let receiveData = urlData {

                let res = response as! NSHTTPURLResponse!

                if 200..<300 ~= res.statusCode {
                    do {
                        jsonData = try NSJSONSerialization.JSONObjectWithData(receiveData, options: NSJSONReadingOptions.init(rawValue:0))

                        completion(jsonData: jsonData, error: nil)
                    } catch let error as NSError {
                        let returnedError = NSError(domain: "validateUser", code: 3, userInfo: [
                            "title": "Made up title",
                            "message": "This is a messsage",
                            "cause": error
                            ])
                        completion(jsonData: nil, error: returnedError)
                    }
                }else{
                    let returnedError = NSError(domain: "validateUser", code: 1, userInfo: [
                        "title": "Second made up title",
                        "message": "This is another message"
                        ])
                    completion(jsonData: nil, error: returnedError)
                }
            }else{

                var userInfo: [NSObject: AnyObject] = [
                    "title": "Third made up title",
                    "message": "This is yet another message"
                ]
                if let error = responseError {
                    userInfo["message"] = error.localizedDescription
                    userInfo["cause"] = error
                }
                let returnedError = NSError(domain: "validateUser", code: 2, userInfo: userInfo)
                completion(jsonData: nil, error: returnedError)
            }


        }
        task.resume()

    }

    func validateUser(location: String, username: String, password: String) {

        let data = "&username=\(username)&password=\(password)"

        self.makeHTTPRequest(data, location: location) { jsonData, error in

            if let json = jsonData {

                self.jsonObj = json


                print(self.jsonObj)   // This shows property was assigned without errors

            }else{
                let userInfo = error!.userInfo
                let title = userInfo["title"] as! String
                let message = userInfo["message"] as! String
                print(title)
                print(message)
            }
        }
    }
}

这是我在validatUser()调用validatUser()方法的函数

@IBAction func login(sender: AnyObject) {

        let service = NetworkConnection()
        service.validateUser("http://myPhpServiceLink.com/mobile.login.php", username: usernameField.text!, password: passwordField.text!)

        if let serviceObj = service.jsonObj {

            print("success loading object \(serviceObj)")

        } else {

            print("error loading object from call \(service.jsonObj)")

        }
}

这是PHP要返回的JSON数据。

{"id":"1","username":"admin","message":"User is valid","error":null}

行： print("service object = \\(self.jsonObj)")在控制台中输出以下内容：

service object = Optional({
     error = "<null>";
     id = 1;
     message = "User is valid";
     username = admin;
})

但是我从@IBAction函数得到“从调用nil加载错误的对象”。 我到处寻找以找出为什么该属性在外部调用时总是返回nil ，并且也很难阐明我的问题。

Answer 1

我敢打赌这是由于您的http请求是在后台执行的。
if let serviceObj = service.jsonObj在您的validateUser方法完成之前正在执行if let serviceObj = service.jsonObj 。 您需要重写`valdiateUser以获取完成处理程序。